In the field of semiconductor technology, the performance of a component depends strongly, among other things, on its admissible operating temperatures. A very frequent cause of failure is temperatures that are too high during operation, which are able to damage the component severely or completely destroy it. Therefore, both for the user who has to select suitable semiconductor components for a certain application, and for a manufacturer who has to make specifications for the development of such an element, and also for the manufacturer who specifies his product, the knowledge of the temperature of the component, which sets in under certain usage conditions, is of great interest.
Other systems characterize the temperature of a semiconductor component via the so-called barrier layer temperature Tj, which may be determined, for example, by measuring the forward voltage of pn junctions of a component. (These are junctions between p-doped and n-doped areas of a semiconductor; they are, for instance, components of rectifier and Zener diodes or are present in the form of an intrinsic body diode of a field-effect transistor). In this context, one makes use of the fact that the voltage Uflow, which has to be applied to a pn junction in the flow direction in order to let a certain current I flow, is a function of the crystal temperature at the location of the pn junction. Via the functional connection Uflow(I,Tj), by measuring the forward voltage Uflow for a given current flow I, one may conclude what temperature Tj is.
However, for this one has to know the function Uflow(I,Tj), which is generally ascertained by a preceding stationary calibration measurement of Uflow(I,Tj).
According to the conventional method, measuring current I is sent via the component in flow direction. This method may not be used as long as another operating state of the component prevents this forward current (e.g. during an avalanche breakdown or the like). In addition, in complex integrated circuits the problem may arise that, in general, the transmission states of different semiconductor junctions in the component are not able to be set completely independently of one another. Therefore, the case may arise in which there is an interest in measuring the temperature of a certain pn junction which, however, under normal operating conditions of the component is transparent only transiently. In such a case it is not possible to perform ahead of time a stationary calibration at the pn junction.
These peculiarities of the conventional method lead to the method not being usable, for example, for the investigation of the barrier breakdown (avalanche effect) of a diode. The avalanche state is characterized in that, in the reverse direction, such a high voltage is present that the diode breaks down and a large current flows in the reverse direction (so-called Zener breakdown of a diode). The high fields and currents in general lead to strong heating of the component, the hottest spot is at the pn junction breaking down. In order to determine the temperature prevailing there, using the conventional forward voltage method, one has to wait, however, until the barrier current has decayed almost completely, in order then to conduct a measuring current through the pn junction in the opposite direction. The result of this is that the conventional method is first able to be used after a certain time delay after the decay of the Zener breakdown. The temperature present at this point in time, to be sure, no longer corresponds to the temperature spike at the pn junction that appears during the breakdown, but mostly to a clearly lower temperature, because, between the end of the avalanche state and the beginning of the measurement, the heat may distribute itself already from the region of the pn junction to a larger region of the component or even to the thermally interfaced environment of the component. However, in general it is the transient temperature spikes which lead to damage of the component.
To be sure, the possibility exists of gaining insight concerning the temperature development in the semiconductor component by following the development over time of the forward current after a Zener breakdown, and, by extrapolating this development to points in time before the measurement, of coming to a conclusion on the temperature which could have been prevalent at the time of the breakdown at the interface. However, this method is encumbered with considerable uncertainties. One reason for this is the shortness of the measuring times available and thus the limited accuracy of the temperature measurement which is the more extreme the higher the required temporal resolution; for another reason, there is a fundamental problem in that, by the forward current measurement, only one average value of the temperature is able to be ascertained over the entire surface of the pn junction, but that it is not at all certain that the avalanche current, and thus the temperature distribution in the avalanche state, is uniformly distributed over the junction surface.